Muhammad Ali was the greatest global sports star of the 20th century. He was a beloved figure who transcended boxing.
So it was brutally painful for fans to watch the punishment he absorbed in his last two comebacks against Larry Holmes and Trevor Berbick. With the serious health problems he's had in the years since his retirement, it's hard not look at the last years of Ali's career with regret.
For the most part, great boxing stars earn the right to stick around the sport for as long as they want. But that doesn't mean it's always a good idea.
It can be embarrassing to be an aging athlete who can no longer return a serve or get around on a fastball. It can be dangerous to be an aging boxer who climbs back into the ring too many times.
Ray Leonard retired and came back four times during his career. He originally retired at the very top of his game in 1982, still four years short of 30, citing a damaged retina.
Leonard came back for the first time in 1984, recording a Round 9 TKO of Kevin Howard. Leonard looked far less than spectacular and quickly retired once more.
Then in 1987, Leonard made one of the greatest comebacks in boxing history. After five years almost completely inactive, Leonard came back to face fellow superstar Marvin Hagler for the undisputed middleweight crown. In a close and still-debated fight, Leonard walked away with a split-decision victory.
Leonard followed that by stopping Donny Lalonde to capture the WBC super middleweight and light heavyweight titles, making him a nominal five-division champion. He fought a third fight with Roberto Duran, earning a unanimous decision, and a long-awaited rematch with Tommy Hearns, that went down as a controversial draw which a majority of fans thought Hearns should have won.
Leonard retired for a third time in 1989, only to return in 1991 to face tough young champion Terry Norris. Leonard was knocked down twice and took a beating.
Leonard's third comeback was ill-advised, but not enough to get him on this list. However, in 1999 he returned for a fourth time, at age 40, to face Hector Camacho.
This time Leonard suffered a Round 5 TKO. It was completely unnecessary punishment for him to absorb and a regrettable loss on his resume.
Jerry Quarry was a durable and courageous heavyweight contender during the division's golden era of the 1970s. But after suffering brutal Round 5 TKO losses to Joe Frazier in 1974 and Ken Norton in 1975, he hung up his gloves for two years.
In 1977, he returned for one fight, then went back into retirement until 1983, when he came back to win a pair of fights over trial-horse competitors.
A fighter with a heart like Quarry's is never going to go away easily, but his last return in 1992 at age 47 was definitely regrettable. Quarry dropped a six-round decision to 3-4-1 Ron Cranmer. It was a tough way to see a minor legend go out.
Quarry died just over six years later, in 1999.
Ricky Hatton is one of the biggest boxing stars of the past decade. The Fighting Pride of Manchester, England has as devoted a fanbase as has existed in this century, outside of possibly Manny Pacquiao's armies.
He had a great run that included world titles in two divisions and ran his record to 43-0 before dropping a pair of tough stoppage losses to Floyd Mayweather and Manny Pacquiao in 2007 and 2009.
The Pacquiao KO was particularly brutal, and Hatton retired following it.
Hatton had already become among the biggest boxing stars in the history of his nation and had a promising career started as a promoter. But he couldn't stay away from the ring.
After over three years away, he returned in November 2012 to face Vyacheslav Senchenko. Hatton had ballooned up to 200 pounds or better in his retirement, and he looked like a shadow of his old self after the time away.
Hatton looked like a skilled fighter, but hardly his old self. In Round 9 he went down to a body-punch KO and promptly returned to retirement.
Jermain Taylor was an undisputed middleweight champion of the world and a legitimate star in his prime. But at this point, he's a fighter who needs to walk away before he receives permanent damage.
Taylor was an original entrant in the Showtime Super Six, Super Middleweight tournament, and in October 2009, he received a frightening Round 12 KO from Arthur Abraham. Taylor withdrew from the tournament and stayed inactive for over two years.
Taylor never officially retired, and in December 2011, he finally came back to the ring. In the history of boxing, many fighters have returned from worse head injuries, often sooner. But the results have all too often been tragic.
This is a different era, with advanced awareness of what cumulative head trauma can lead to. Taylor has been successful so far in all four of his comeback fights against guys he could nearly beat in his sleep.
Taylor is a grown man and has the right to do what he wants in his career. But after all he's accomplished anyway, it seems a shame to see him taking this kind of risk.
Iran Barkley is no Hall of Famer, but he was a very nice boxer in his prime. The world middleweight champion beat Tommy Hearns twice and once by TKO. Barkley's split-decision loss to Roberto Duran in 1989 was the Fight of the Year.
But by the mid 1990s, he was pretty much done as a contender.
I don't think Iran Barkley ever officially retired and came back. But there's no question that he's a championship-level boxer who hung around way too long.
By the final two years of his career, 1998 and 1999, he was campaigning as a heavyweight, going 1-7-1. For a fighter who gave so much to the sport, it's tragic how little Barkley was left with in the end.
When Riddick Bowe captured the undisputed heavyweight championship from Evander Holyfield in one of the decade's best fights in November 1992, I felt like I was watching a guy who would eventually become a top-10, all-time heavyweight champion.
Somehow, it didn't work out that way. Less than a month after winning the title, Bowe avoided what would have been an epic showdown with Lennox Lewis by tossing the WBC belt into the trash at a press conference.
After taking a beating in a pair of DQ victories over the wild Andrew Golota in 1996, Bowe retired from the sport. He enlisted in the Marines but lasted just three days.
Bowe was later charged in a bizarre kidnapping incident involving his ex-wife and children. Considering that Bowe's brain damage sustained against Golota had been part of his defense in this case, his returns to the ring in 2004, 2005 and 2008 were all pretty ill-advised.
But his comeback in 2013 to test himself in the Muay Thai ring is what earned him his spot on this list. In the video included here, Bowe appears to have very little kickboxing training.
Like Iran Barkley, Roy Jones Jr. is a former middleweight champion who doesn't seem to know when to quit. Unlike Barkley, Jones was the greatest pound-for-pound star of his generation. He was most likely set for life financially before this century even began.
It's been discouraging for fans old enough to remember his prime to watch Jones continue forward, receiving bad head trauma repeatedly.
When Jones lost by a Round 2 TKO to Antonio Tarver in 2004, it seemed likely he just got caught. But when he lost his next fight to Glen Johnson by a Round 9 KO, trailing on the cards, no less, it was obvious that Jones had lost a step.
Jones put together a decent stretch in the middle part of the last decade, losing only to Joe Calzaghe by unanimous decision. But in December 2009, he suffered a devastating first-round TKO to Danny Green.
His KO loss to Denis Lebedev in May 2011 was scary to see.
Jones has come back to win three fights in a row since that stoppage. But it seems like it's only a matter of time before Jones gets unnecessarily put to sleep again.
James J. Jeffries was the fourth man to hold the heavyweight championship of the world during the gloved era. He was a very big heavyweight for his era and an extremely gifted natural athlete.
He dominated his era as thoroughly as almost any champion in history and retired undefeated in 1904.
By 1910, Jack Johnson was reigning as history's first black heavyweight champion of the world. Johnson's very existence was an affront to the racist society of the time, and he did everything he could to rub his success in white America's face.
As Johnson's reign lengthened, writers like Jack London cried out for a "Great White Hope" to take Johnson down. Many eyes began to fall upon Jeffries, now long in retirement and grown fat.
Jeffries' comeback fight against Johnson was one of the major sporting events of the 20th century. But it was completely one-sided.
For coming out of retirement to be racist America's hero, Jim Jeffries got smashed by Round 15 TKO.
I'm not sure it's fair to call Joe Louis' comeback "ill-advised" because the persecution of the IRS really left him little choice. But when Joe Louis retired as heavyweight champion in 1948, he was a national hero and a living symbol of his generation's great triumph over Nazism in World War II.
Louis was a great man and should have been able to retire in dignity. But by 1950, he was back in the ring to challenge champion Ezzard Charles. Louis lost by unanimous decision.
Louis then won eight more fights before facing rising star Rocky Marciano. It was truly a generational crossroads fight, with Louis going down to the younger slugger by a Round 8 TKO.
For a generation of boxing fans, it was heartbreaking to watch.
Most boxing fans who truly revere Muhammad Ali will tell you they wish he had retired after "The Thrilla' in Manila," his grueling third fight with Joe Frazier in 1975. Instead, he fought six times in the next two years, including real battles with Ken Norton, Alfredo Evangelista and Earnie Shavers.
Then, in February 1978, Ali lost one of history's most shocking upsets to Leon Spinks. He returned in September to beat Spinks and become the first ever three-time heavyweight champion. After the fight, he retired.
But by 1980, Ali was back and looking to challenge his heir, Larry Holmes. Holmes was in many important ways a younger version of Ali, and the beating he gave the old champion was predictable and sad. For years as a kid I had an old Inside Sports cover of a battered Ali in his corner taped up on the wall of my room.
Following his Round-10, TKO loss, Ali retired again. But the very next year he came back.
Ali's final comeback just seems like a cruel joke. Even as a 10-year-old boy who idolized him, I knew he had no chance of ever regaining the belt.
In his last hurrah, the greatest heavyweight champion in history went 10 hard rounds while probably already suffering from Parkinson's disease, and lost by unanimous decision to Trevor Berbick, a fighter who hadn't been good enough to serve as one of his sparring partners only five years or so earlier.